The Protein and Biochemistry Core will express and purify proteins for all members of the Program Project. In addition. Core B will perform quantitative analyses of protein-DNA interactions and characterize the kinetic properties of DNA repair proteins using high-throughput fluorimetric assays. Specific Aim 1: (A) To optimize the expression and purification of DNA repair proteins Core B will produce mg amounts of soluble proteins for Projects 1, 2, 3, and 4. We will express the proteins in different E. coli strains using protocols and methods that have proven successful in the past four years in our laboratory, such as autoinduction. We will continue to use limited proteolysis in conjunction with bioinformatics to delineate functional domains and express smaller fragments, if the full-length protein construct fails to overexpress. (B) To optimize the solubility and stability of proteins and complexes to be used in crystallization experiments, by characterizing solvent effects on protein aggregation properties using dynamic light scattering and analytical gel filtration. Crystallization trials using commercial kits will be set up using a robotic workstation. Specific Aim 2: To perform rapid quantitative analyses of protein-DNA interactions and steady-state enzyme kinetic properties of wild-type and mutant DNA repair enzymes generated in this Program Project, using high-throughput fluorimetric assays